1. Field of the Invention
The present invention is directed to a digital oscillation generator that, in particular, is suitable for employment in a radio-frequency transmitter of a diagnostic magnetic resonance apparatus.
2. Description of the Prior Art
In magnetic resonance imaging, the frequency dependency of the magnetic resonance signals on the magnetic field is utilized for the spatial resolution. Given the imaging sequences that are currently standard, a magnetic field gradient is produced in the imaging region in addition to the main magnetic field such that only nuclei in a specific slice of a subject are excited. For the excitation of the slice, a radio-frequency signal having a corresponding center frequency and bandwidth is transmitted into a region to be imaged. The spatial resolution in the slice ensues by a subsequent phase encoding and, upon reception of the magnetic resonance signals, by a frequency encoding with corresponding magnetic field gradients.
U.S. Pat. No. 5,170,123 discloses a magnetic resonance apparatus with a digital transmitter/receiver. The digital transmitter/receiver has a numerically controlled modulation oscillator (NCMO) whose frequency and phrase can be predetermined with digital control signals that are generated by a sequence controller. A further input is provided for lowering the base frequency. The output of the numerically controlled modulation oscillator is a value with which a sine table in a following memory is addressed. The output signal is then supplied to a modulator in the transmitter and to a demodulator in the receiver.